Internal problem ID [1366]
Internal file name [OUTPUT/1367_Sunday_June_05_2022_02_13_26_AM_29279783/index.tex]
Book: Elementary differential equations with boundary value problems. William F. Trench.
Brooks/Cole 2001
Section: Chapter 7 Series Solutions of Linear Second Equations. 7.6 THE METHOD OF
FROBENIUS II. Exercises 7.6. Page 374
Problem number: 14.
ODE order: 2.
ODE degree: 1.
The type(s) of ODE detected by this program : "second order series method. Regular singular point. Repeated root"
Maple gives the following as the ode type
[[_2nd_order, _with_linear_symmetries]]
\[ \boxed {x^{2} \left (1+x \right ) y^{\prime \prime }-x \left (3-x \right ) y^{\prime }+4 y=0} \] With the expansion point for the power series method at \(x = 0\).
The type of the expansion point is first determined. This is done on the homogeneous part of the ODE. \[ \left (x^{3}+x^{2}\right ) y^{\prime \prime }+\left (x^{2}-3 x \right ) y^{\prime }+4 y = 0 \] The following is summary of singularities for the above ode. Writing the ode as \begin {align*} y^{\prime \prime }+p(x) y^{\prime } + q(x) y &=0 \end {align*}
Where \begin {align*} p(x) &= \frac {x -3}{x \left (1+x \right )}\\ q(x) &= \frac {4}{x^{2} \left (1+x \right )}\\ \end {align*}
| \(p(x)=\frac {x -3}{x \left (1+x \right )}\) | |
| singularity | type |
| \(x = -1\) | \(\text {``regular''}\) |
| \(x = 0\) | \(\text {``regular''}\) |
| \(q(x)=\frac {4}{x^{2} \left (1+x \right )}\) | |
| singularity | type |
| \(x = -1\) | \(\text {``regular''}\) |
| \(x = 0\) | \(\text {``regular''}\) |
Combining everything together gives the following summary of singularities for the ode as
Regular singular points : \([-1, 0, \infty ]\)
Irregular singular points : \([]\)
Since \(x = 0\) is regular singular point, then Frobenius power series is used. The ode is normalized to be \[ x^{2} \left (1+x \right ) y^{\prime \prime }+\left (x^{2}-3 x \right ) y^{\prime }+4 y = 0 \] Let the solution be represented as Frobenius power series of the form \[ y = \moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r} \] Then \begin{align*} y^{\prime } &= \moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) a_{n} x^{n +r -1} \\ y^{\prime \prime } &= \moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) \left (n +r -1\right ) a_{n} x^{n +r -2} \\ \end{align*} Substituting the above back into the ode gives \begin{equation} \tag{1} x^{2} \left (1+x \right ) \left (\moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) \left (n +r -1\right ) a_{n} x^{n +r -2}\right )+\left (x^{2}-3 x \right ) \left (\moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) a_{n} x^{n +r -1}\right )+4 \left (\moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r}\right ) = 0 \end{equation} Which simplifies to \begin{equation} \tag{2A} \left (\moverset {\infty }{\munderset {n =0}{\sum }}x^{1+n +r} a_{n} \left (n +r \right ) \left (n +r -1\right )\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}x^{n +r} a_{n} \left (n +r \right ) \left (n +r -1\right )\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}x^{1+n +r} a_{n} \left (n +r \right )\right )+\moverset {\infty }{\munderset {n =0}{\sum }}\left (-3 x^{n +r} a_{n} \left (n +r \right )\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}4 a_{n} x^{n +r}\right ) = 0 \end{equation} The next step is to make all powers of \(x\) be \(n +r\) in each summation term. Going over each summation term above with power of \(x\) in it which is not already \(x^{n +r}\) and adjusting the power and the corresponding index gives \begin{align*} \moverset {\infty }{\munderset {n =0}{\sum }}x^{1+n +r} a_{n} \left (n +r \right ) \left (n +r -1\right ) &= \moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} \left (n +r -1\right ) \left (n +r -2\right ) x^{n +r} \\ \moverset {\infty }{\munderset {n =0}{\sum }}x^{1+n +r} a_{n} \left (n +r \right ) &= \moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} \left (n +r -1\right ) x^{n +r} \\ \end{align*} Substituting all the above in Eq (2A) gives the following equation where now all powers of \(x\) are the same and equal to \(n +r\). \begin{equation} \tag{2B} \left (\moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} \left (n +r -1\right ) \left (n +r -2\right ) x^{n +r}\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}x^{n +r} a_{n} \left (n +r \right ) \left (n +r -1\right )\right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} \left (n +r -1\right ) x^{n +r}\right )+\moverset {\infty }{\munderset {n =0}{\sum }}\left (-3 x^{n +r} a_{n} \left (n +r \right )\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}4 a_{n} x^{n +r}\right ) = 0 \end{equation} The indicial equation is obtained from \(n = 0\). From Eq (2B) this gives \[ x^{n +r} a_{n} \left (n +r \right ) \left (n +r -1\right )-3 x^{n +r} a_{n} \left (n +r \right )+4 a_{n} x^{n +r} = 0 \] When \(n = 0\) the above becomes \[ x^{r} a_{0} r \left (-1+r \right )-3 x^{r} a_{0} r +4 a_{0} x^{r} = 0 \] Or \[ \left (x^{r} r \left (-1+r \right )-3 x^{r} r +4 x^{r}\right ) a_{0} = 0 \] Since \(a_{0}\neq 0\) then the above simplifies to \[ \left (r -2\right )^{2} x^{r} = 0 \] Since the above is true for all \(x\) then the indicial equation becomes \[ \left (r -2\right )^{2} = 0 \] Solving for \(r\) gives the roots of the indicial equation as \begin {align*} r_1 &= 2\\ r_2 &= 2 \end {align*}
Since \(a_{0}\neq 0\) then the indicial equation becomes \[ \left (r -2\right )^{2} x^{r} = 0 \] Solving for \(r\) gives the roots of the indicial equation as \([2, 2]\).
Since the root of the indicial equation is repeated, then we can construct two linearly independent solutions. The first solution has the form \begin {align*} y_{1}\left (x \right ) &= \moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r}\tag {1A} \end {align*}
Now the second solution \(y_{2}\) is found using \begin {align*} y_{2}\left (x \right ) &= y_{1}\left (x \right ) \ln \left (x \right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}b_{n} x^{n +r}\right )\tag {1B} \end {align*}
Then the general solution will be \[ y = c_{1} y_{1}\left (x \right )+c_{2} y_{2}\left (x \right ) \] In Eq (1B) the sum starts from 1 and not zero. In Eq (1A), \(a_{0}\) is never zero, and is arbitrary and is typically taken as \(a_{0} = 1\), and \(\{c_{1}, c_{2}\}\) are two arbitray constants of integration which can be found from initial conditions. Using the value of the indicial root found earlier, \(r = 2\), Eqs (1A,1B) become \begin {align*} y_{1}\left (x \right ) &= \moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +2}\\ y_{2}\left (x \right ) &= y_{1}\left (x \right ) \ln \left (x \right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}b_{n} x^{n +2}\right ) \end {align*}
We start by finding the first solution \(y_{1}\left (x \right )\). Eq (2B) derived above is now used to find all \(a_{n}\) coefficients. The case \(n = 0\) is skipped since it was used to find the roots of the indicial equation. \(a_{0}\) is arbitrary and taken as \(a_{0} = 1\). For \(1\le n\) the recursive equation is \begin{equation} \tag{3} a_{n -1} \left (n +r -1\right ) \left (n +r -2\right )+a_{n} \left (n +r \right ) \left (n +r -1\right )+a_{n -1} \left (n +r -1\right )-3 a_{n} \left (n +r \right )+4 a_{n} = 0 \end{equation} Solving for \(a_{n}\) from recursive equation (4) gives \[ a_{n} = -\frac {a_{n -1} \left (n^{2}+2 n r +r^{2}-2 n -2 r +1\right )}{n^{2}+2 n r +r^{2}-4 n -4 r +4}\tag {4} \] Which for the root \(r = 2\) becomes \[ a_{n} = -\frac {a_{n -1} \left (1+n \right )^{2}}{n^{2}}\tag {5} \] At this point, it is a good idea to keep track of \(a_{n}\) in a table both before substituting \(r = 2\) and after as more terms are found using the above recursive equation.
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
For \(n = 1\), using the above recursive equation gives \[ a_{1}=-\frac {r^{2}}{\left (-1+r \right )^{2}} \] Which for the root \(r = 2\) becomes \[ a_{1}=-4 \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {r^{2}}{\left (-1+r \right )^{2}}\) | \(-4\) |
For \(n = 2\), using the above recursive equation gives \[ a_{2}=\frac {\left (1+r \right )^{2}}{\left (-1+r \right )^{2}} \] Which for the root \(r = 2\) becomes \[ a_{2}=9 \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {r^{2}}{\left (-1+r \right )^{2}}\) | \(-4\) |
| \(a_{2}\) | \(\frac {\left (1+r \right )^{2}}{\left (-1+r \right )^{2}}\) | \(9\) |
For \(n = 3\), using the above recursive equation gives \[ a_{3}=-\frac {\left (r +2\right )^{2}}{\left (-1+r \right )^{2}} \] Which for the root \(r = 2\) becomes \[ a_{3}=-16 \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {r^{2}}{\left (-1+r \right )^{2}}\) | \(-4\) |
| \(a_{2}\) | \(\frac {\left (1+r \right )^{2}}{\left (-1+r \right )^{2}}\) | \(9\) |
| \(a_{3}\) | \(-\frac {\left (r +2\right )^{2}}{\left (-1+r \right )^{2}}\) | \(-16\) |
For \(n = 4\), using the above recursive equation gives \[ a_{4}=\frac {\left (r +3\right )^{2}}{\left (-1+r \right )^{2}} \] Which for the root \(r = 2\) becomes \[ a_{4}=25 \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {r^{2}}{\left (-1+r \right )^{2}}\) | \(-4\) |
| \(a_{2}\) | \(\frac {\left (1+r \right )^{2}}{\left (-1+r \right )^{2}}\) | \(9\) |
| \(a_{3}\) | \(-\frac {\left (r +2\right )^{2}}{\left (-1+r \right )^{2}}\) | \(-16\) |
| \(a_{4}\) | \(\frac {\left (r +3\right )^{2}}{\left (-1+r \right )^{2}}\) | \(25\) |
For \(n = 5\), using the above recursive equation gives \[ a_{5}=-\frac {\left (r +4\right )^{2}}{\left (-1+r \right )^{2}} \] Which for the root \(r = 2\) becomes \[ a_{5}=-36 \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {r^{2}}{\left (-1+r \right )^{2}}\) | \(-4\) |
| \(a_{2}\) | \(\frac {\left (1+r \right )^{2}}{\left (-1+r \right )^{2}}\) | \(9\) |
| \(a_{3}\) | \(-\frac {\left (r +2\right )^{2}}{\left (-1+r \right )^{2}}\) | \(-16\) |
| \(a_{4}\) | \(\frac {\left (r +3\right )^{2}}{\left (-1+r \right )^{2}}\) | \(25\) |
| \(a_{5}\) | \(-\frac {\left (r +4\right )^{2}}{\left (-1+r \right )^{2}}\) | \(-36\) |
Using the above table, then the first solution \(y_{1}\left (x \right )\) is \begin{align*} y_{1}\left (x \right )&= x^{2} \left (a_{0}+a_{1} x +a_{2} x^{2}+a_{3} x^{3}+a_{4} x^{4}+a_{5} x^{5}+a_{6} x^{6}\dots \right ) \\ &= x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right ) \\ \end{align*} Now the second solution is found. The second solution is given by \[ y_{2}\left (x \right ) = y_{1}\left (x \right ) \ln \left (x \right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}b_{n} x^{n +r}\right ) \] Where \(b_{n}\) is found using \[ b_{n} = \frac {d}{d r}a_{n ,r} \] And the above is then evaluated at \(r = 2\). The above table for \(a_{n ,r}\) is used for this purpose. Computing the derivatives gives the following table
| \(n\) | \(b_{n ,r}\) | \(a_{n}\) | \(b_{n ,r} = \frac {d}{d r}a_{n ,r}\) | \(b_{n}\left (r =2\right )\) |
| \(b_{0}\) | \(1\) | \(1\) | N/A since \(b_{n}\) starts from 1 | N/A |
| \(b_{1}\) | \(-\frac {r^{2}}{\left (-1+r \right )^{2}}\) | \(-4\) | \(\frac {2 r}{\left (-1+r \right )^{3}}\) | \(4\) |
| \(b_{2}\) | \(\frac {\left (1+r \right )^{2}}{\left (-1+r \right )^{2}}\) | \(9\) | \(\frac {-4-4 r}{\left (-1+r \right )^{3}}\) | \(-12\) |
| \(b_{3}\) | \(-\frac {\left (r +2\right )^{2}}{\left (-1+r \right )^{2}}\) | \(-16\) | \(\frac {6 r +12}{\left (-1+r \right )^{3}}\) | \(24\) |
| \(b_{4}\) | \(\frac {\left (r +3\right )^{2}}{\left (-1+r \right )^{2}}\) | \(25\) | \(\frac {-8 r -24}{\left (-1+r \right )^{3}}\) | \(-40\) |
| \(b_{5}\) | \(-\frac {\left (r +4\right )^{2}}{\left (-1+r \right )^{2}}\) | \(-36\) | \(\frac {10 r +40}{\left (-1+r \right )^{3}}\) | \(60\) |
The above table gives all values of \(b_{n}\) needed. Hence the second solution is \begin{align*} y_{2}\left (x \right )&=y_{1}\left (x \right ) \ln \left (x \right )+b_{0}+b_{1} x +b_{2} x^{2}+b_{3} x^{3}+b_{4} x^{4}+b_{5} x^{5}+b_{6} x^{6}\dots \\ &= x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right ) \ln \left (x \right )+x^{2} \left (60 x^{5}-40 x^{4}+24 x^{3}-12 x^{2}+4 x +O\left (x^{6}\right )\right ) \\ \end{align*} Therefore the homogeneous solution is \begin{align*} y_h(x) &= c_{1} y_{1}\left (x \right )+c_{2} y_{2}\left (x \right ) \\ &= c_{1} x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right ) + c_{2} \left (x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right ) \ln \left (x \right )+x^{2} \left (60 x^{5}-40 x^{4}+24 x^{3}-12 x^{2}+4 x +O\left (x^{6}\right )\right )\right ) \\ \end{align*} Hence the final solution is \begin{align*} y &= y_h \\ &= c_{1} x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right )+c_{2} \left (x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right ) \ln \left (x \right )+x^{2} \left (60 x^{5}-40 x^{4}+24 x^{3}-12 x^{2}+4 x +O\left (x^{6}\right )\right )\right ) \\ \end{align*}
The solution(s) found are the following \begin{align*} \tag{1} y &= c_{1} x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right )+c_{2} \left (x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right ) \ln \left (x \right )+x^{2} \left (60 x^{5}-40 x^{4}+24 x^{3}-12 x^{2}+4 x +O\left (x^{6}\right )\right )\right ) \\ \end{align*}
Verification of solutions
\[ y = c_{1} x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right )+c_{2} \left (x^{2} \left (-36 x^{5}+25 x^{4}-16 x^{3}+9 x^{2}-4 x +1+O\left (x^{6}\right )\right ) \ln \left (x \right )+x^{2} \left (60 x^{5}-40 x^{4}+24 x^{3}-12 x^{2}+4 x +O\left (x^{6}\right )\right )\right ) \] Verified OK.
\[ \begin {array}{lll} & {} & \textrm {Let's solve}\hspace {3pt} \\ {} & {} & x^{2} \left (1+x \right ) \left (\frac {d}{d x}y^{\prime }\right )+\left (x^{2}-3 x \right ) y^{\prime }+4 y=0 \\ \bullet & {} & \textrm {Highest derivative means the order of the ODE is}\hspace {3pt} 2 \\ {} & {} & \frac {d}{d x}y^{\prime } \\ \bullet & {} & \textrm {Isolate 2nd derivative}\hspace {3pt} \\ {} & {} & \frac {d}{d x}y^{\prime }=-\frac {4 y}{x^{2} \left (1+x \right )}-\frac {\left (x -3\right ) y^{\prime }}{x \left (1+x \right )} \\ \bullet & {} & \textrm {Group terms with}\hspace {3pt} y\hspace {3pt}\textrm {on the lhs of the ODE and the rest on the rhs of the ODE; ODE is linear}\hspace {3pt} \\ {} & {} & \frac {d}{d x}y^{\prime }+\frac {\left (x -3\right ) y^{\prime }}{x \left (1+x \right )}+\frac {4 y}{x^{2} \left (1+x \right )}=0 \\ \square & {} & \textrm {Check to see if}\hspace {3pt} x_{0}\hspace {3pt}\textrm {is a regular singular point}\hspace {3pt} \\ {} & \circ & \textrm {Define functions}\hspace {3pt} \\ {} & {} & \left [P_{2}\left (x \right )=\frac {x -3}{x \left (1+x \right )}, P_{3}\left (x \right )=\frac {4}{x^{2} \left (1+x \right )}\right ] \\ {} & \circ & \left (1+x \right )\cdot P_{2}\left (x \right )\textrm {is analytic at}\hspace {3pt} x =-1 \\ {} & {} & \left (\left (1+x \right )\cdot P_{2}\left (x \right )\right )\bigg | {\mstack {}{_{x \hiderel {=}-1}}}=4 \\ {} & \circ & \left (1+x \right )^{2}\cdot P_{3}\left (x \right )\textrm {is analytic at}\hspace {3pt} x =-1 \\ {} & {} & \left (\left (1+x \right )^{2}\cdot P_{3}\left (x \right )\right )\bigg | {\mstack {}{_{x \hiderel {=}-1}}}=0 \\ {} & \circ & x =-1\textrm {is a regular singular point}\hspace {3pt} \\ & {} & \textrm {Check to see if}\hspace {3pt} x_{0}\hspace {3pt}\textrm {is a regular singular point}\hspace {3pt} \\ {} & {} & x_{0}=-1 \\ \bullet & {} & \textrm {Multiply by denominators}\hspace {3pt} \\ {} & {} & x^{2} \left (1+x \right ) \left (\frac {d}{d x}y^{\prime }\right )+x \left (x -3\right ) y^{\prime }+4 y=0 \\ \bullet & {} & \textrm {Change variables using}\hspace {3pt} x =u -1\hspace {3pt}\textrm {so that the regular singular point is at}\hspace {3pt} u =0 \\ {} & {} & \left (u^{3}-2 u^{2}+u \right ) \left (\frac {d}{d u}\frac {d}{d u}y \left (u \right )\right )+\left (u^{2}-5 u +4\right ) \left (\frac {d}{d u}y \left (u \right )\right )+4 y \left (u \right )=0 \\ \bullet & {} & \textrm {Assume series solution for}\hspace {3pt} y \left (u \right ) \\ {} & {} & y \left (u \right )=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} u^{k +r} \\ \square & {} & \textrm {Rewrite ODE with series expansions}\hspace {3pt} \\ {} & \circ & \textrm {Convert}\hspace {3pt} u^{m}\cdot \left (\frac {d}{d u}y \left (u \right )\right )\hspace {3pt}\textrm {to series expansion for}\hspace {3pt} m =0..2 \\ {} & {} & u^{m}\cdot \left (\frac {d}{d u}y \left (u \right )\right )=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} \left (k +r \right ) u^{k +r -1+m} \\ {} & \circ & \textrm {Shift index using}\hspace {3pt} k \mathrm {->}k +1-m \\ {} & {} & u^{m}\cdot \left (\frac {d}{d u}y \left (u \right )\right )=\moverset {\infty }{\munderset {k =-1+m}{\sum }}a_{k +1-m} \left (k +1-m +r \right ) u^{k +r} \\ {} & \circ & \textrm {Convert}\hspace {3pt} u^{m}\cdot \left (\frac {d}{d u}\frac {d}{d u}y \left (u \right )\right )\hspace {3pt}\textrm {to series expansion for}\hspace {3pt} m =1..3 \\ {} & {} & u^{m}\cdot \left (\frac {d}{d u}\frac {d}{d u}y \left (u \right )\right )=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} \left (k +r \right ) \left (k +r -1\right ) u^{k +r -2+m} \\ {} & \circ & \textrm {Shift index using}\hspace {3pt} k \mathrm {->}k +2-m \\ {} & {} & u^{m}\cdot \left (\frac {d}{d u}\frac {d}{d u}y \left (u \right )\right )=\moverset {\infty }{\munderset {k =-2+m}{\sum }}a_{k +2-m} \left (k +2-m +r \right ) \left (k +1-m +r \right ) u^{k +r} \\ & {} & \textrm {Rewrite ODE with series expansions}\hspace {3pt} \\ {} & {} & a_{0} r \left (3+r \right ) u^{-1+r}+\left (a_{1} \left (1+r \right ) \left (4+r \right )-a_{0} \left (2 r^{2}+3 r -4\right )\right ) u^{r}+\left (\moverset {\infty }{\munderset {k =1}{\sum }}\left (a_{k +1} \left (k +1+r \right ) \left (k +4+r \right )-a_{k} \left (2 k^{2}+4 k r +2 r^{2}+3 k +3 r -4\right )+a_{k -1} \left (k +r -1\right )^{2}\right ) u^{k +r}\right )=0 \\ \bullet & {} & a_{0}\textrm {cannot be 0 by assumption, giving the indicial equation}\hspace {3pt} \\ {} & {} & r \left (3+r \right )=0 \\ \bullet & {} & \textrm {Values of r that satisfy the indicial equation}\hspace {3pt} \\ {} & {} & r \in \left \{-3, 0\right \} \\ \bullet & {} & \textrm {Each term must be 0}\hspace {3pt} \\ {} & {} & a_{1} \left (1+r \right ) \left (4+r \right )-a_{0} \left (2 r^{2}+3 r -4\right )=0 \\ \bullet & {} & \textrm {Each term in the series must be 0, giving the recursion relation}\hspace {3pt} \\ {} & {} & a_{k +1} \left (k +1+r \right ) \left (k +4+r \right )-a_{k} \left (2 k^{2}+4 k r +2 r^{2}+3 k +3 r -4\right )+a_{k -1} \left (k +r -1\right )^{2}=0 \\ \bullet & {} & \textrm {Shift index using}\hspace {3pt} k \mathrm {->}k +1 \\ {} & {} & a_{k +2} \left (k +2+r \right ) \left (k +5+r \right )-a_{k +1} \left (2 \left (k +1\right )^{2}+4 \left (k +1\right ) r +2 r^{2}+3 k -1+3 r \right )+a_{k} \left (k +r \right )^{2}=0 \\ \bullet & {} & \textrm {Recursion relation that defines series solution to ODE}\hspace {3pt} \\ {} & {} & a_{k +2}=-\frac {k^{2} a_{k}-2 k^{2} a_{k +1}+2 k r a_{k}-4 k r a_{k +1}+r^{2} a_{k}-2 r^{2} a_{k +1}-7 k a_{k +1}-7 r a_{k +1}-a_{k +1}}{\left (k +2+r \right ) \left (k +5+r \right )} \\ \bullet & {} & \textrm {Recursion relation for}\hspace {3pt} r =-3 \\ {} & {} & a_{k +2}=-\frac {k^{2} a_{k}-2 k^{2} a_{k +1}-6 k a_{k}+5 k a_{k +1}+9 a_{k}+2 a_{k +1}}{\left (k -1\right ) \left (k +2\right )} \\ \bullet & {} & \textrm {Series not valid for}\hspace {3pt} r =-3\hspace {3pt}\textrm {, division by}\hspace {3pt} 0\hspace {3pt}\textrm {in the recursion relation at}\hspace {3pt} k =1 \\ {} & {} & a_{k +2}=-\frac {k^{2} a_{k}-2 k^{2} a_{k +1}-6 k a_{k}+5 k a_{k +1}+9 a_{k}+2 a_{k +1}}{\left (k -1\right ) \left (k +2\right )} \\ \bullet & {} & \textrm {Recursion relation for}\hspace {3pt} r =0 \\ {} & {} & a_{k +2}=-\frac {k^{2} a_{k}-2 k^{2} a_{k +1}-7 k a_{k +1}-a_{k +1}}{\left (k +2\right ) \left (k +5\right )} \\ \bullet & {} & \textrm {Solution for}\hspace {3pt} r =0 \\ {} & {} & \left [y \left (u \right )=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} u^{k}, a_{k +2}=-\frac {k^{2} a_{k}-2 k^{2} a_{k +1}-7 k a_{k +1}-a_{k +1}}{\left (k +2\right ) \left (k +5\right )}, 4 a_{1}+4 a_{0}=0\right ] \\ \bullet & {} & \textrm {Revert the change of variables}\hspace {3pt} u =1+x \\ {} & {} & \left [y=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} \left (1+x \right )^{k}, a_{k +2}=-\frac {k^{2} a_{k}-2 k^{2} a_{k +1}-7 k a_{k +1}-a_{k +1}}{\left (k +2\right ) \left (k +5\right )}, 4 a_{1}+4 a_{0}=0\right ] \end {array} \]
Maple trace Kovacic algorithm successful
`Methods for second order ODEs: --- Trying classification methods --- trying a quadrature checking if the LODE has constant coefficients checking if the LODE is of Euler type trying a symmetry of the form [xi=0, eta=F(x)] checking if the LODE is missing y -> Trying a Liouvillian solution using Kovacics algorithm A Liouvillian solution exists Reducible group (found an exponential solution) Group is reducible, not completely reducible <- Kovacics algorithm successful`
✓ Solution by Maple
Time used: 0.016 (sec). Leaf size: 69
Order:=6; dsolve(x^2*(1+x)*diff(y(x),x$2)-x*(3-x)*diff(y(x),x)+4*y(x)=0,y(x),type='series',x=0);
\[ y \left (x \right ) = x^{2} \left (\left (c_{2} \ln \left (x \right )+c_{1} \right ) \left (1-4 x +9 x^{2}-16 x^{3}+25 x^{4}-36 x^{5}+\operatorname {O}\left (x^{6}\right )\right )+\left (4 x -12 x^{2}+24 x^{3}-40 x^{4}+60 x^{5}+\operatorname {O}\left (x^{6}\right )\right ) c_{2} \right ) \]
✓ Solution by Mathematica
Time used: 0.007 (sec). Leaf size: 98
AsymptoticDSolveValue[x^2*(1+x)*y''[x]-x*(3-x)*y'[x]+4*y[x]==0,y[x],{x,0,5}]
\[ y(x)\to c_1 \left (-36 x^5+25 x^4-16 x^3+9 x^2-4 x+1\right ) x^2+c_2 \left (\left (60 x^5-40 x^4+24 x^3-12 x^2+4 x\right ) x^2+\left (-36 x^5+25 x^4-16 x^3+9 x^2-4 x+1\right ) x^2 \log (x)\right ) \]